1. Field of the Invention
This invention relates generally to write-once, read-only semiconductor memory arrays and, more specifically, to lower power write-once, read-only semiconductor memory arrays including semiconductor devices and fabrication methods therefor.
2. Description of the Prior Art
In the past, manufacturers of semiconductor write-once, read-only (PROM) memory arrays have sought ways of producing lower power semiconductor memory arrays in order to permit users of these arrays to operate them with much lower power.
One recent technique that has been implemented by some semiconductor circuit manufacturers to provide low power semiconductor circuits has been to use high resistivity resistors in place of conventional resistors used in the circuit in order to reduce the power needed to operate the circuits. However, prior attempts to improve circuit operation by developing semiconductor circuits that operate with lower power have not been very satisfactory due to the difficulty in forming high resistivity, shallow semiconductor resistor regions. For example, diffused semiconductor resistors were found to be undesirable due to the fact that the graded diffused region after diffusing through an opening in the silicon dioxide layer into the bare silicon generally created very deep semiconductor regions which reduced the resistivity of these resistor regions because resistivity is inversely proportional to region thickness.
Prior attempts to produce high resistivity ion implanted semiconductor resistor regions have not been successful because these ion implanted semiconductor resistor regions were performed through openings in the silicon dioxide surface layer thereby causing relatively deep semiconductor resistor regions which lowered the resistance of these semiconductor regions.
Attempts at making shallow P type diffused or implanted regions with Boron through openings in the silicon dioxide layer were not successful because of the fact that Boron outdiffused into the thermally grown silicon dioxide layer thereby resulting in the loss of the initially formed, shallow, high resistivity Boron doped resistor region.
Accordingly, a need existed to provide a low power programmable read-only semiconductor memory array which would have very shallow, high resistivity semiconductor resistor regions or structures to thereby lower the power needed to operate the semiconductor PROM.